Gaffey, a retired chief engineer of Bell Helicopter, is seeking partners to launch the project in advance of a potential competition to replace the US Army's Bell OH-58D Kiowa Warrior.

AVX's concept is based on modifying the current aircraft with a coaxial rotor for lift and two ducted fans mounted on a shortened tail boom for thrust and yaw control.

The flight controls would be modified by adding a control device to the collective that would allow the pilot to transfer as much as 70% of engine power from the rotor to the ducted fans in forward flight, Gaffey says. The new device is currently a twist grip, but that could change as the design evolves, he adds.

The ducted fans would help increase the OH-58's maximum speed with a full payload from about 90kt (166km/h) to 120kt, Gaffey says. The more efficient lift provided by the coaxial rotor system would also allows the aircraft to hover out of ground effect at 6,000ft (1,830m) in temperatures up to 35°C (95°F).

Gaffey says he considers the concept a "low-risk" alternative to replacing the army's OH-58s, but acknowledges two engineering concerns. The design team must overcome the potential problem of complex aerodynamic interactions between the coaxial rotor and ducted fan system, and the airframe must handle a higher vibration load, he says. The AVX design reuses the OH-58's existing vibration cancellation system.

AVX launched in 2005 to develop a coaxial-rotor flying car, with start-up financing from Denver-based attorney David Brody, Gaffey says. The company turned its focus to the OH-58 replacement after the flying car project stalled.

AVX suppliers include Rotating Composites for the fans, Aurora Flight Sciences for the ducts, Eagle Aviation Technologies for the drive system and transmission and Advanced Technologies for the rotor hubs.

The company needs to raise $30 million to launch a proof-of-concept demonstration using a Bell 206, with first flight possible within 18 months. It plans to offer the product to the army as a $1.5 million kit upgrade, with a non-recurring engineering bill amortised over 360 aircraft of $250,000 each, Gaffey says.